Escalier

Escalier : Un escalier est une construction architecturale constituée d’une suite régulière de marches, ou degrés, permettant d’accéder à un étage, de passer d’un niveau à un autre en montant et descendant. Le terme a une origine étymologique latine, scala signifiant échelle. Le métier correspondant est celui d’escaliéteur.
Par extension, ce type de construction a donné son nom à un escalier, voie piétonne, à ciel ouvert ou couverte, constituée d’une ou plusieurs marches. Escalier sur Wikipédia (fr) 

Stairs : Stairs are a structure designed to bridge a large vertical distance between lower and higher levels by dividing it into smaller vertical distances. This is achieved as a diagonal series of horizontal platforms called steps which enable passage to the other level by stepping from one to another step in turn. Steps are very typically rectangular, but may instead be straight, curved, or may consist of two or more straight pieces connected at angles.
Types of stairs include staircases (also called stairways) and escalators. Some alternatives to stairs are elevators (also called lifts), stairlifts, inclined moving walkways, ladders, and ramps. A stairwell is a vertical shaft or opening that contains a staircase. A flight (of stairs) is an inclined part of a staircase consisting of steps (and their lateral supports if supports are separate from steps). Stairs sur Wikipédia (en)